Variable electrical resistor



Jan. 4, 1949. L. STRAUB ETAL 2,458,314

VARIABLE ELECTRICAL RESISTOR Filed Jan. 11, 194s s Shets-Sheet 1 v Van-l 06E/YE 4, 575 9 5 Inventors PET/10 E-c. ZEN V57 Attorney Jan. 4,1949. E. STRAUB ET AL 2,458,314

VARIABLE ELECTRICAL RESISTOR Filed Jan. 11, 1946 5 Shets-Sheet 2 504mm?.4. STRH gI E/IC DPS Mar/leg Jan. 4, 1949. E. sTRAUB EI 'AL 2,458,314

VARIABLE ELECTRICAL RESISTOR Filed Jan. ll, 1946 3 Sheets-Sheet 3Patented Jan. 4, 1949 VARIABLE ELECTRICAL RESISTOR Eugene LeopoldStraub, Wembley Hill, and

Arthur Edward Charles Bennett, Kenton, England, assignors to DubilierCondenser Company (1925) Limited, London England, a company of GreatBritain Application January 11, 1946, Serial No. 640,490 In GreatBritain January 18, 1945 3 Claims. 1

This invention relates to variable electrical resistors and is moreparticularly concerned with small resistors, such as are commonlyemployed as volume controls in wireless receivers.

When such resistors are called upon to withstand frequent relativelylarge temperature cycles, and the combination of high temperatures andhigh humidity which are found in tropical climates, it is essential forthem to be protected against the ingress of moisture and otherwise to beso constructed that the moving contacts and the cooperatin resistanceelement will not be exposed to moisture. The main object of the presentinvention is to provide a simple and relatively cheap construction ofhermetically sealed variable resistor which permits a standard resistorsuitable for temperate climates to be used and does not entail specialconstruction of the complete device.

The improved resistor according to the invention is hermetically sealedfor operation under tropical conditions by enclosure in a metal casinghaving one closed end through which extends an adjusting spindle for theresistor whilst the other end of the casing is closed by a sealing discof rubber or water-resisting rubber-like material, through which extendleads to the resistor, this end of the casing being hermetically sealedby resiliently pressing into the outer surface of the sealing disc boththe edge of the easing and the flanges or rims of tubular rivets oreyelets fixed to the leads, so that the sealing disc is compressed anddeformed to provide waterprooi' joints between the rubber and the metalpressed into it. Preferably the casing is cupshaped and may, forexample, be of aluminium, or other non-brittle metal.

This form of sealing is particularly applicable to so-called miniatureconstruction and in the improved resistor according to the present invention, which enables the dimensions to be very considerably reduced ascompared with normal construction, the resistor element is supported bythe casing sealing disc whilst the adjusting spindle, carrying a movingcontact for engaging the e ement, is carried by a bearing on the closedend of the casing so that the casing itself, which is cup-shaped, actsas the mechanical supporting structure of the resistor.

The invention may be carried into practice in various ways, but twoconvenient practical arrangements, each according to the invention, areshown by way of example and as applied to a volume control in theaccompanying drawings, in which Figure 1 shows one construction in sideelevation,

Figure 2 is an exploded longitudinal section on the line IIII of Figure4, but on a larger scale,

Figure 3 is a section on the line III-III of Figure 2,

Figure 4 is a section on the line IVIV of Figure 2,

Figure 5 illustrates the resistor in end elevation from right to left ofFigure 1,

Figure 6 is a diagrammatic representation of the electrical connectionswithin the resistor casing,

Figure 7 is a fragmentary section through a modified form of scaling forthe electric leads where they extend through the end discs,

Figure 8 illustrates a modified arrangement of the sealing rings betweenthe adjusting spindle and its bearing,

Figure 9 is a View, similar to that of Figure 1, of a modifiedconstruction of resistor,

Figure 10 shows the resistor in end elevation from right to left ofFigure 9,

Figure 11 is a view, similar to that of Figure 2, of the modifiedconstruction shown in Figures 9 and 10 but on a larger scale,

Figures 12, 13 and 14 are sections on the lines XII-XII, XIII-XIII andXIV-XIV of Figure 11 respectively,

Figure 15 is a diagrammatic representation of the electrical connectionswithin the casing of the resistor shown in Figures 9 to 14 inclusive,and

Figures 16 and 1? illustrate two modified forms of tubular rivet whichmay be employed with either of the constructions above described.

In the construction shown in Figures 1 to 6 the resistor itself is ofthe usual type consisting of a disc A of rigid insulating materialhaving on one surface a resistance element B consisting of a fiat stripof conducting resistor material, such for example as a carbon compound,shaped as an annulus but with a break to provide two ends B1, B2 whichare spaced from one another and are respectively connected throughrivets B3, B4 to two terminal tags B5, B6 lying in recesses B7 in thedisc A. A moving contact C, consisting of several springy fingers orwires, is resiliently pressed into contact with the strip B and issupported on an insulating contact arm C1 carried at one end of aspindle D extending through a bore in the centre of the disc A. A mainbearing the recess or indentation F2 on that side thereof remote fromthe strip B. The adjusting spindle D projects beyond the end of thebearing E and, when assembled, has an operating knob D1 secured thereto.A sliding contact is provided between a metallic annulus C2,carried-'by'the contact arm C1 and connected to the spring contact Cthrough a metal strip anchored to the arm C1 by a rivet C3, and abifurcated springy contact C4 connected through a rivet C5 to a thirdterminal tag Cs lying in one of the recesses B7 of the disc .A.The-spindle 3D is held in position in the bearing -E, soithat there isappropriate pressure between the contacts "B, C and C2, C4, by a Cwasher D2 which clips into an annular groove D3 in the spindle D andthus forms a flange-like abutment bearingagainst the outer end of thebearing boss E. The outside of the bearing boss E is screwthreaded toreceive a collar E1 wh ch is screwed on to the bearing'boss E so asfirmly to clamp the resistor unit within the metal casing F.

In order, in accordance with the invention, to make such resistor tropc-proof, it is enclosed inthemetal casing'F which is substantiallycupshaped and has a holeF1 in'its closed end through which projects thespindle D and a part of the bearing boss E. Athin annular ring'G1 'of'insulating material, for example of fibre, elephantide or similarmaterial, "and of a diameter slightly less than the internal diameter ofthe casing F, is inserted in the casing'before the resistor'is assembledin the casing F and'serves to prevent metallic contact between thecasing F and any of the terminal tags B5, B6, C6 on the main resistordisc A.

The jo nt-between theedge of the hole'F1 in-the end of the "casing "Fand the bearing boss 'E is hermetically sealed. When'the-metal of thecasing F and the boss E can readily be-soldered, this seal can beeffected by running solder around the ed e of theholeFl after theresistor isin posit on. When, however, as isusual andpreferable, thecasing F is of aluminium, andthus cannot eas ly be soldered, thehermetic seal is provided by compressing, between'the insulating disc G1and the inside of the end of the casing F, 'a'washer Gof rubberorawater-resistingrubber-like material, such'for exampleasthesynthetic-rubber neoprene. The rubber washer G is inserted on to'thebearing boss'E a'fterthe-insulating disc G1, and the *casing F iscountersunkto form'a recess F2 around 'the inside of the hole F1 so thatthe washer G is trapped in the annular recess thereby "preventing orreducing outwardradial 'expansion of the washer when it is axiallycompressed. The washer G is compressed, so as to render the'jointmoisture-proor and water-proof, "by the'collar E1 which, whentightened, draws the resistor towards the end. of the casing F'so that"the "washer G is compressed between the disc A an'dthe sai'den'd df'thecasing. Theradial inward expansion of the washer G 'as a "result of th scompression will cause the washer G 'to "tighten 'on"to"the"boss E,thereby assisting in'the sealing 'against ingress *of moisture.

An additional indentation- Fe is provided adjacent to 'the outer rim ofthe casing F and projecting outwardly to a greater extent than Therelative depths of the two indentations are preferably such' that -whenthe collar E1-is clamped'up tightly'its outer face is approximatelylevel with the outer indentation F6. "The outer end surface of thecasing F of the complete resistor-can thus be pressed against thesurface of the :panel idndicated at "1) on which it is mounted. A nut E2on the threaded boss E enables the user of the component to clamp it onto the panel T.

The disc A of the resistor unit itself with the interposed insulatingwasher G1, bears against the annular surface Fzbeing clamped thereto bythe collar E1. The insulating washer G1 is preferably arranged to fitover the outside of the resilient washer G which thus bears directlyagainst the more moisture impervious moulded disc A.

:disc Hrbeing engaged by an annular indentation or shoulder F4formednear the rim of thecasing Flby'spinning or other. suitable shapingoperation. The hermetic seal is obtained by spinning over the riinFs ofthe casing F so that it presses into and deforms the outer surface ofthe rubber, or

rubber-like, sealing disc H without perforating it. The leads J, J1, J2to the three terminal tags B5, B6, Ce also extend through spaced holesin the discs H, H1. :throughthe two discs I-I, H1, the edges of theThree tubular rivets K extend outertfianges of the rivets being pressedinto the outer surface of the rubberdisc H so as to deform it .and thusform a water and moisture-proof joint a's in the case of the joint F5 atthe rim of the casing F. The leads J, J1, J2 extend axially through therivets K and are sealed therein by solder K1 which also closes the boresof the rivets K. Alternatively, each lead J3 (Figure 7) may havedishedmetal eyelets or washers K2 soldered thereto after assembly, theedge of each outer washer'Kz being-resiliently pressed into the outersurface of the disc H to-effect the requisite seal. In order that thebearing for the spindle D "may also act as asealing gland, the spindleis provided with'an annular groove D4 which, prior 'to assembly, isfilled with a water-resistant oil -or-grease which serves also as alubricant. addition, the spindle D has formed therein two annularretaining grooves D5 on opposite sides respectively of the groove D4.Each groove D5 has "fitted therein a ring or washer D6 of water-'res'istant rubber-like material, such, for example,

as neoprene-or'hycar-or, the internal diameter of the ring D6 being lessthan the diameter at the bottomofthe associated groove D5 whilst theexternal diameter of the ring is slightly greater than the internaldiameter of the boss E. The ringsDs'arepreferably of a'synthetic rubbersuch for example as neoprene, or any other suitable rubber-like materialpossessing adequate oil resistance which will prevent deterioration bythe oil or grease-spreading over the surface of the spindle 'and'itshearing from the groove D4. Thus, :on assembly, the resilient rings Degrip the spindle and are radially compressed between the spindle D andthe bore of the bearing boss E and, though permitting free rotation ofthe spindle D, assist the action of the oil channel D4 to prevent theingress of moisture. Instead of the retaining grooves being formed inthe spindle D, grooves D7 (Figure 8) may be formed in the boss E inaddition to the oil channel D4 in the spindle D, the external diameterof each resilient ring De being greater than the diameter at the bottomof the associated groove D7 whilst the internal diameter of the ring isslightly less than the diameter of the spindle D.

In order to limit the angular movement of the spindle D, and thereforethe travel of the moving contact C over the resistor element B, anabutment A1 formed integral with the disc A cooperates with a stud A2carried by the spindle D.

The construction above described particularly lends itself for mountingwithin the containers or casings of radio sets or other apparatus, whichcasings are sealed against ingress of moisture. To this end a ring ofneoprene or other suitable material may be arranged in the recess F7(Figures 2 and 3) so that when the nut E2 outside the casing istightened the said ring is compressed and held against lateral expansionby the recess F1. This ring thereby seals the opening in the casingthrough which the boss E extends.

In the modified construction shown in Figures 9 to 15, the dimensionsmay be very considerably reduced as compared with normal constructionsof resistor or volume control, the resistor element L being supported bythe rigid insulating backing disc M associated with the rubber, orrubber-like, sealing disc N. The adjusting spindle O, carrying themoving contact 01 for bearing against the strip resistor element L, isjournalled in a bearing boss P formed integral with the closed end wallR1 of the metal casing R. Thus, the casing R itself, which is cup-shapedas shown in Figure 11, acts as the mechanical supporting structure forthe resistor. With this construction the casing R and the boss P may beformed in two parts of brass, soldered together to form a hermetic seal,in which case they may conveniently be tin plated or cadmium plated toincrease their resistance to corrosion by damp atmospheres.Alternatively, these two parts may be formed integrally together as forexample by an extrusion process, in which case they may for example beconstructed of hard aluminium, or aluminium a1- loy. As clearly shown inFigure 12, the strip-type resistor element L, formed as an annulus witha break in it, lies on, or in a recess in, the inner face of the rigiddisc M which backs the rubberlike sealing disc N. The three leads Q1,Q2, Q extend into three tubular rivets Q3, Q4, Q5 respectively, eachrivet. extending through the two discs M and N. The two rivets Q3, Q4are electrically connected respectively to the two ends of the resistorelement L and secure the resistor ele- M ment to the rigid disc M(Figures 12 and 15), whilst the third rivet Q5 is electrically connectedto a bifurcated springy contact member whose two arms S carry contactsS1 both of which bear against a metal plate 02 lying on, or in a recessin, the outer surface of the insulating disc 03 within which theadjusting spindle O is moulded. The moving contact 01 is constituted bya tongue struck upwards from the plate 02, as shown in Figure 13, theplate being secured to the disc 03 by integral tongues 01 on the plate02 extending through notches O5 in the disc 03 and being clinched overbehind the disc, as shown in Figure 14. A stop R2 formed within thecasing R cooperates with a rib 06 formed on the disc or block 03 so asto limit the angular rotation of the spindle O and therefore themovement of the contact 01 over the resistor element L.

The moving contact 01 and the contacts S,

vS1 may be of any suitabe form to provide a good and durable rubbingcontact with the resistor element L and the plate 02 respectively, butpreferably these contacts are of stiff springy metal which may be platedwith silver, nickel or other non-rusting metal, a cup or pimple beingpressed out at or near the ends of each contact arm to provide a curvedprofile for engaging the cooperating surface L or 02.

Alternatively the contact 01 may be duplicate so as to provde a dualpoint of contact with the element L, a second tongue being struckupwards from the plate 02 for this purpose so that the second contactlies closely adjacent to the first one. According to a furtherarrangement a multiple wire contact shimilar to that shown in Figure 2and secured to the plate 02 may be employed. Such multiple contacts arepreferably arranged so that their points of contact with the resistorelement L are made substantially on a radial line.

The seal at one end of the casing is eifected as described withreference to Figure 2, that is to say by pressing the outer flanges ofthe rivets Q3, Q4, Q5 into the outer surface of the rubberlike sealingdisc N and then soldering the leads to close the outer ends of therivets as indicated at Q6. At the other end of the casing R, the boss Pis externally screw-threaded to receive the clamping nut T1 by which theresistor is locked to the panel T, whilst the adjusting spindie is heldin position by a C washer T2, as above described. Alternatively, thespindle 0 may be provided with a collar or the equivalent at its innerend which engages the inside of the casing R (or the insulating block 03may serve this purpose).

It will be appreciated that the dimensions of the various parts are suchthat when the end discs M and N are fitted on and the edge of the casingR spun over to effect hermetic sealing, the moving contact 01 bearsagainst the element L with the appropriate pressure whilst the contactsS1 press against the plate 02.

The bearing of the spindle O is sealed by means of the oil groove V andthe two retaining grooves V1 containing the compressible rings V2, asdescribed with reference to Figure 2, through the arrangement of Figure8 may be employed.

Instead of the tubular rivets K or Q3, Q4, Q5 described above each rivetmay be formed with a tubular socket W (Figure 16) at its inner end forriveting over and soldering on to the associated lead within the casing,an intermediate integral rib W1 being turned or pressed on the rivet forclinching over into the outer surface of the resilient sealing disc H orN. The outer end of the rivet has either a solder tag W2, as shown inFigure 16, or a screwthreaded stub W3 (which may itself have a soldertag) for receiving a terminal nut We as shown in Figure 17.

It has been found from comprehensive tests that the improved volumecontrol according to the invention is not only capable of withstandingnormal tropical tests but can in fact withstand a temperature of C. at100% relative humidity for prolonged periods without any moisturepenetrating the casing. It will also withstand continuous immersion inwater for substantial periods without leakage into this casing.

Moreover, the construction of Figures 9 to 15 has a minimum of partswhich are so arranged as to facilitate midget construction. Thus, forexample, with this construction a tropic-proof r'netically sealed.

volume control having the characteristics normally required for wirelessreceivers may have a casing less thanthree-quarters of an inch indiameter and less than half an inch long. A further -advantage of theconstruction, in addition to the very great reduction in size ascompared with normal volume controls, is the improved heat dissipationobtained by the use of -.the metal casing as the main mechanicalsupporting structure.

It will be understood that the constructions above described are givenby way of example only and that details'may be made, within the scope ofthe invention, to suit the form and use of the resistor. Thus, forexample, whilst the invention has been described as applied to a volumecontrol of the circular type with a flat strip composition element, theresistor body may be ofvany other convenient Shape and the element maybe disposed in any other convenient manner, for example edgewise, andmay consist of a conducting composition or may be wire- -wound.- It isalso to be understood that where practicable any suitable materialsother "than those specifically mentioned may be used.

What we claim as our invention and desire to secure by Letters Patentis:

l; A variable electrical resistor comprising a cup-like aluminium casingopen at one end and having anapertured end wall at the other end, anaxially bored and externally screwthreaded bearin boss extending throughsaid aperture, an

insulating body secured to the boss within the casing, a rotaryadjusting spindle within the bearing boss and extending through theinsulating body into the casing, an annular groove, for containingsealing oil o'r' grease, formed in the part of the spindle lyingwithin'the bearing, two supplementary annular grooves formed in thespindle on opposite sides of said oil groove respectively, rings ofresilient rnaterial located in ing, the rubber washer being compressedbetween the base of said recess and'the insulating washer when theclamping nut is tightened to draw the insulating body towards the saidcasing end wall,

a resilient sealing disc closing the said open end of the casing, arigid backing disc of insuating material arranged against the inner faceof said sealing disc, the rim at the open end of the casmg being spuninto a bead housing the edge portions of the sealing and backing discswith the edge of said rim pressed into the outer surface of the sealingdisc without perforating the disc, thereby hermetically sealing thejoint between thecasing and the discs, three tubular rivets extendingthrough apertures in the discs, and three electric leads extendingrespectively into the rivets and electrically connected to the movingcontact operated by the spindle and to the two ends of the resistorelement, the outermost flanges of the rivets being pressed into theouter surface ofthe sealing disc whilst the leads'are soldered in therivets whose bores are thus her- 8 "2'. A variable"electri'c'al resistorcomprising a cup-like aluminium casing open at one end-arid having anapertured end wall at the other end, an axially bored and: externallyscrewthreaded bearing boss formed integral with the casing andprojecting "axially :from the said end wall thereof,

a rotary adjusting spindle within the bearing boss andextending'into thecasing, an annular groove, for containing sealing oil or grease, formedin thepart'of the spindle lying within the bearing, two supplementaryannular grooves formedin the spindle on opposite sides respectively ofsaid oil groove, resilient rings locatedin said supplementary groovesand compressed between the spindle and the bearing bore, an insulatingbody carried at the inner end of the spindle within the'casing, a'metalend plate carried'on the inner face of the *saidinsulating body, amoving contactcons'tithted-by "an integral tongue struck-up fromsaidendplate, a resilient sealing disc closing the open end of the casing, arigid insulating backing disc arranged onthe inner face of the sealingdisc, the rim at the open end of the -casin -being spun into a beadhousing the edges of the sealing and backing discs with the edge of saidrim pressed into the outer surface of the sealing disc withoutperforating the disc, thereby hermetically sealing the 'joint betweenthe casing and the sealing disc, a strip resistor element carried on theinner face of'th'e backing disc, three tubular rivets extending throughapertures in the discs, three electric leads extending into the tubularrivets respectively and soldered therein so as to seal the bores of therivets whose outer flanges or heads are pressed into theoutersurfa'ce ofthe sealing disc withoutperforatin the disc, thereby hermetiresilientlyagainst the metal end plate of the spindlewhilstthe moving contactoperated by the spindlebears resiliently against the resistor element.

3. A variable electrical resistor comprising a metal casing open at (Oneend and having an :apertured end wall at the other end, an external,-

ly-screwt'hreaded and axially bored bearing boss extending through'thehole in said end wallfia rotary adjusting spindle-extending through thebore of said boss, at least one grease retaining annular groove beingformed between the spindle and the said boss whilst at least onesupplementary annular groove is formed between the spindle and the boss,a radia ly compressible sealing washer in said supplementary groove, aninsulating block carried by the bearing boss within the casing, a movingcontact carried by the spindle within the casing, a resistance elementcarriedby said block and engaged by said moving contact, anaxially'compressible resilient washer embracing said bearing boss andlocated in a recess formed in the end wall of the casing, a locking nutengaging said external thread onth'e bearing-boss-outside the end wallof the casing, said nut causing the said resilient washer to be axiallycompressed in said recess between the end wall of the casing and saidinsulating block whereby the compressible washer seals the joint betweenthe insulating block and the end wall of the casing, a sealing disc ofresilient moisture- 75 resistin material aclo'sing the said open :end ofthe casing, a rigid insulating backing disc arranged against the innersurface of the sealing disc, the rim of the casing being spun into abead forming a shoulder abutting said backing disc whilst the said rimis spun inwards and pressed inwards into the outer surface of thesealing disc without perforatin the disc, thereby sealing the jointbetween the casing and the sealing disc, three axially bored rivets inalignment with apertures extending through the sealing and backingdiscs, three electric leads extending into the said rivets whose rimsare bent over and pressed into the outer surface of the sealing discthereby sealing the joints between the rivets and the sealing disc,means Within the casing connecting two of said leads to opposite endsrespectively of the resistance element, and means Within the casingconnecting the third lead to said moving contact.

EUGENE LEOPOLD STRAUB.

ARTHUR EDWARD CHARLES BENNETT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,160,142 Hathorn May 30, 19392,358,991 Miller Sept. 26, 1944 FOREIGN PATENTS Number Country Date473,402 Great Britain Oct. 12, 1937

